1 

MEMORANDUM 

TO: Air and Radiation Docket EPA-HQ-OAR-2012-0401 

FROM: EPA Office of Transportation and Air Quality 

DATE: May 20, 2013 

SUBJECT: Cellulosic Content of Various Feedstocks 

This memorandum provides information on EPA’s evaluation of components generally found in 

feedstocks that would be used to produce cellulosic biofuels. As discussed in the Preamblea, we 

find that no feedstock contains exclusively cellulose, hemicellulose and lignin. This is not 

surprising since all organisms require other types of molecules, including proteins, membrane 

lipids, starches, and DNA/RNA, to fulfill essential functions of the cell such as enzymatic 

catalysis of biochemical reactions, energy storage and coding of genetic information. However, 

we find that all of the biomass generally considered “cellulosic” feedstocks, including corn 

stover and switchgrass, contain greater than 70% of their biomass carbon in cellulose, 

hemicellulose and lignin, and most of these feedstocks contain 85-90% cellulosic components. 

A. BACKGROUND 

The “cellulosic components” of feedstock consist of the major structural components: cellulose, 

hemicellulose, and lignin. These materials are also referred to as “lignocellulosic”. They are 

known as structural components because they are the main components of plant cell walls that 

provide strength, mechanical support and protection to the cell. These components can be 

defined as follows1: 

 

a

 Regulation of Fuels and Fuel Additives: RFS Pathways II and Technical Amendments to the RFS 2 Standards, 

Section V.A.1.
2 

 Cellulose — A structural carbohydrate that is the principal constituent of wood and other 

biomass. It is a polymer of glucose with a repeating unit of C6H10O5 strung together by ßglycosidic linkages. 

 Hemicellulose — A structural carbohydrate that consists of short, highly branched chains 

of sugars. In contrast to cellulose, which is a polymer of only glucose, a hemicellulose is 

a polymer of multiple different sugars, including five-carbon sugars (usually D-xylose 

and L-arabinose), six-carbon sugars (D-galactose, D-glucose, and D-mannose) and uronic 

acid. The sugars are highly substituted with acetic acid. 

 Lignin — The major noncarbohydrate structural constituent of plant biomass, lignin is an 

irregular polymer that gives plant cells much of their mechanical strength. It has a large, 

complex, cross-linked, and highly aromatic structure derived principally from coniferyl 

alcohol (C10H12O3). Because of its extensive cross-linking and complex chemical 

structure, lignin is very difficult to break down biochemically. 

Biomass also includes other organic compounds that perform essential functions in the cells, 

including energy storage, enzymatic catalysis of biochemical reactions and selective transport of 

molecules into or out of the cellb. These other compounds include but are not restricted to: 

 Extractives — Any number of different compounds in biomass that are not an integral 

part of the cellular structure. The compounds can be extracted from biomass by means of 

polar and non-polar solvents including hot or cold water, ether, benzene, methanol and 

other solvents. The types of extractives found in biomass samples may include free 

sugars, pigments, membrane lipids, oils, and many other compounds. 

 Protein — A protein molecule is a chain of up to several hundred amino acids that is 

folded into a more or less compact structure. Because about 20 different amino acids are 

 

b

 Feedstocks also contain inorganic components often referred to as “ash” which do not contribute to biofuel 

produced. 
3 

used by living matter in making proteins, the variety of protein types is enormous. In 

their biologically active states, proteins function as catalysts in metabolism and to some 

extent as structural elements of cells and tissues. 

 Starch — A molecule composed of long chains of -glucose molecules linked together. 

These linkages occur in chains of -1,4 linkages with branches formed as a result of -

1,6 linkages. This polysaccharide is widely distributed in the vegetable kingdom and is 

stored in all grains and tubers. Starch is highly amorphous, making it readily attacked by 

human and animal enzyme systems and broken down into glucose. 

There is significant variation in the data reported on feedstock component compositions (see for 

example data on corn stover in Table 1), due in part to the natural heterogeneity of plants, much 

of which may result from: 

 Differences between different varieties or species within a generic feedstock type2, 

 Variability in the environmental conditions where the feedstock was grown2, 

 Sampling of different parts of the plant which may have different composition (e.g. 

whole plant versus stalks and leaves),2

 Harvesting of the feedstock at different stages of maturity,3

 Variability in feedstock composition in different years,2

 Differences in the agronomic practices used to grow the crop,2 and 

 Degradation or alteration of the biomass during storage.4

Additional apparent variability may appear if comparing results determined using different 

analytical methods or even from variability between analytical batches in the same laboratory.5

Examination of one research study provides an example of both the compositional variability 

observed within one feedstock and of how different factors may contribute to this variability. 

This study analyzed the composition of 508 commercial hybrid corn stover samples collected 

from 47 sites in 8 states over 3 harvest years. 2 Glucan composition (a proxy for cellulose 

content) in these samples varied by more than 10% of the total mass, ranging from 26.5% to 

37.6% of total mass (Table 1). Lignin concentrations fell between 11.2% and 17.8% of total 

mass. Standard deviations (as percentages) for the three major components were 5% for 
4 

hemicellulose, 6% for cellulose and 8% for lignin, indicating that most of the measurements fell 

within more narrow ranges. Standard deviations for the minor components (extractives, protein 

and inorganics/ash) are relatively larger, ranging from 16% for ash to 22% for protein. The 

authors found that harvest year was the largest source of variability, probably reflecting the 

important influence of weather on composition. Within a given sample year, environmental 

factors such as soil type and weather appeared to account for more variability than did the corn 

hybrid variety, although the hybrid variety also affected the variability in composition. 

It is likely that variability when comparing different studies would be greater than that observed 

for this one study because of differences in the analytical methods used, as well as due to other 

factors that this study controlled for such as the part of the plant used and how the material was 

stored. Accordingly, this study likely underestimates the amount of variability we could expect 

to see in our comparison. 

The purpose of this document is to present EPA’s understanding of the cellulosic content of 

different biofuel feedstocks. Given the variability in the data, we report ranges whenever 

available. We also take a consistent approach to looking at the data (described in the next 

section). The data itself we grouped into broad categories including cellulosic components 

(cellulose, hemicellulose and lignin), other organics (extractives, protein), and inorganics 

(inorganics, ash). Each of these main components has sub-components as described in the 

following section. More detailed information about each analysis is available in a spreadsheet 

posted on the docket.c

 

 

c

 “Cellulosic Content of Various Feedstocks Spreadsheet – for the docket”, which has been placed in docket EPAHQ-OAR-2012-0401. 
5 

Table 1. Average biochemical composition of corn stover based on 508 samples from 47 

sites in 8 states over 3 harvest years, including the standard deviation and range of the 

estimates. 2 Values labeled “Reported” are as reported in the paper. Values labeled 

“Used” are the values used in our analysis, which are calculated as described in the text 

based on the reported values. 

*Standard deviation calculated by propagation of error. 

 

Average Std. Dev. Range

Cellulose

Reported: Glucan 31.9 2.0 26.5‐37.6

Used: Total Cellulose 31.9 2.0

Hemicellulose

Reported: Xylan 18.9 1.3 14.8‐22.7

Galactan 1.5 0.2 0.8‐1.9

Arabinan 2.8 0.3 1.6‐3.6

Mannan 0.3 0.1 0.0‐0.7

Acetyl 2.2 0.3 0.9‐2.9

Used: Total Hemicellulose 25.7 1.4

Lignin

Reported: Lignin 13.3 1.1 11.2‐17.8

Used: Total Lignin 13.3 1.1

Extractives

Reported: Ethanol solubles 3.3 0.4 1.7‐4.1

Sucrose 3.6 2.1 ‐1.0‐10.0

Water‐extractible (other) 8.6 2.3 1.4‐15.7

Used: Total extractives (organic) 15.5 3.1

Protein

Reported: Protein 3.7 0.8 1.1‐5.4

Used: Protein 3.7 0.8

Inorganics/Ash

Extractible inorganics (soil) 2.5 0.5 0.0‐4.8

Structural inorganics (ash) 3.9 0.9 0.8‐6.6

Used: Total inorganics 6.4 1.0

Percent Recovery

Reported: Component closure 96.4 1.6

Used: % Recovery 96.4 1.6

Cellulosic Composition

Cellulosic Components 70.9 2.7

Other Organics 19.2 3.2

Inorganics(Ash) 6.4 1.0

Adjusted Cellulosic Composition 78.6 3.3*

* 

* 

* 

* 

* 

* 
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B. EPA’S APPROACH 

In order to determine what percentage of feedstocks typically considered “cellulosic”, such as 

corn stover and switchgrass, is composed of cellulose, hemicellulose and lignin, EPA surveyed 

the scientific literature to assemble a range of estimates of the composition of different 

feedstocks. To do this, we reviewed 12 scientific publications, reports or communications and 

the DOE Biomass online database. Most of the studies used some version of the procedure 

outlined by the National Renewable Energy Laboratory’s (NREL) Standard Biomass Analytical 

Procedure.6

 These procedures involve separation of extractives followed by determination of 

structural components via a two-stage sulfuric acid hydrolysis, followed by analysis of the 

individual sugars via HPLC. Lignin is measured in the acid soluble and acid insoluble fractions. 

Proteins are determined based on the nitrogen content of the material, and ash content is 

determined after heating of the sample. One study used near-infrared spectroscopy (NIRS) / 

partial least squares modeling, calibrated with the NREL methods. An accompanying 

spreadsheet lists the methods used for each study, along with the compounds reported by the 

authors and how EPA made its calculations based on this reported data.d

As discussed, Table 1 shows how EPA combined the data reported in one paper into the values 

used for our analysis. Some of the studies reported a concentration for “cellulose” or 

“hemicellulose”, but most reported concentrations for the individual sugars that comprise these 

biomolecules. For example, most studies report a concentration for glucan or glucose, almost all 

of which is contained in cellulose. We assumed that the concentration of cellulose was 

equivalent to the reported concentration of glucan or glucose, as shown in Table 1. This may be 

a slight overestimation since hemicellulose also contains some glucose; however, concentrations 

of glucose in cellulose are likely to dwarf that in hemicellulose, so this approximation should be 

reasonably accurate. For hemicellulose, studies reported some combination of concentrations for 

xylan/xylose, galactan/galactose, arabinan/arabinose, mannan/mannose, rhamnose and fucose, as 

 

d

 “Cellulosic Content of Various Feedstocks Spreadsheet – for the docket”, which has been placed in docket EPAHQ-OAR-2012-0401. 
7 

well as acetyl/acetate and uronic acids. To estimate total hemicellulose concentration, we 

summed the concentrations of these individual components. Note that this value may slightly 

underestimate the true concentration of hemicellulose since it excludes any glucose contained in 

this biomolecule. Lignin was reported as either “lignin”, “Klason lignin” or both “acid soluble 

lignin” and “acid insoluble lignin”. For our estimates, we combined the concentrations of all 

types of lignin reported. One source4 reported only acid detergent lignin (ADL) for a number of 

different feedstocks. This study also stated that acid insoluble lignin (which is generally much 

more concentrated than acid soluble lignin) tends to be 2-4 times more concentrated than ADL 

for grasses, whereas acid insoluble lignin is only about 30% higher than ADL for legumes. 

Accordingly, for these samples, we multiplied the reported ADL value by 3 for grasses and by 

1.3 for legumes. However, this estimate introduces considerable uncertainty into the total 

cellulosic content values, so these numbers should be considered less certain than the other 

values. Studies reported a number of different types of “extractives”, including compounds 

extracted with ethanol, ethanol/toluene, water, and hot water, as well as sucrose, organic acids, 

individual sugars (Glc, Fru, Raf, Sta) and fats/lipids. We added all of these components together 

to estimate the concentration of total extractives. Studies generally determined the concentration 

of protein (if calculated) by multiplying the nitrogen content of the sample (as mass %) by 6.25 

to scale up to total protein content.7 When reporting the total inorganic, or “ash”, content of a 

sample, studies mostly reported one value. However, some studies reported a value for 

extractible inorganics and one for structural inorganics (ash; Table 1). Two studies reported a 

value for “volatile solids”, which is essentially everything but the ash.8,9 For these studies, we 

calculated the ash content by subtracting the volatile solids concentration from 100%. We also 

added together the cellulose, hemicellulose and lignin concentrations to determine the total 

cellulosic concentration, and added protein and extractives together to determine the 

concentration of “other organics”. 

Once we had calculated the concentrations (as mass %) for cellulose, hemicellulose, lignin, 

extractives, protein, and ash, we added these components together to determine the percent 

recovery for each analysis (Table 1). Percent recoveries ranged from 88% to 106%.e

 Recoveries 

 

e

 For studies in which they analyzed all components. Some studies did not report concentrations of protein, 

extractives or ash, in which case percent recoveries were lower. For these cases, we did not adjust the composition 

to adjust for percent recovery. 
8 

may be lower than 100% because of losses during sample processing or because portions of the 

material were not analyzed. Recoveries greater than 100% indicate that one or more analytical 

method used over-reports the amount of material recovered. We adjusted the percent cellulosic 

value to account for the percent recovery: in cases of recoveries greater than 100%, the values 

were adjusted lower; in cases of recoveries less than 100%, values were adjusted higher. We 

also adjusted the cellulosic content to account for the ash content of the feedstock. Inorganic 

(ash) materials are not likely to end up in the final fuel product made from the feedstock, and if 

they did, they would not contribute to the fuel heating content (which is how RINs are 

determined). Our calculations therefore adjusted the final cellulosic composition to reflect the 

percent of the organic (non-ash) component of the feedstock that is cellulose, hemicellulose or 

lignin. The “Adjusted Cellulosic Composition” shown in Table 1 demonstrates the results of the 

adjustments for percent recovery and inorganic content for corn stover from one study, as 

described above. 

C. CELLULOSIC CONCENTRATIONS IN BIOMASS 

EPA considered the component concentrations of several different types of feedstocks, including 

several types of crop residue, grasses including miscanthus and switchgrass, a variety of woods 

and branches, based on the categories of “cellulosic” feedstocks included in Table 1 to CFR § 

80.1426. Data derived from twelve different scientific publications, reports or communications 

and from the Department of Energy’s Biomass Feedstock Composition and Property Database,

which contains compositional data for over 150 feedstock samples.10 Because of the high degree 

of natural variability in biomass (discussed above), the average compositions are likely more 

meaningful than any single value reported. This is because no single value can reflect the 

compositional range and variability present in that type of biomass, particularly if this value 

derives from a small number of samples. However, examination of the range of values observed 

and the average values calculated should provide insight into the degree of variability present, as 

well as the most common composition, and thus be more informative. The data are summarized 
9 

in Tables 2-4, and a more detailed presentation of the data reported in each paper and EPA’s use 

of this data can be found in an accompanying spreadsheetf. 

a. Crop Residue 

EPA found information about the biochemical composition of a number of types of crop residue, 

including corn stover, sugarcane bagasse, and straw from wheat, rice, soybeans, rye and barley 

(Table 2). Of these, corn stover is widely considered to be the predominant choice of crop 

residue for biomass production. As shown in Table 2, EPA examined data on the composition of 

corn stover from four different sources. Based on the reported data, cellulosic components 

comprised between 71 and 83% of the total mass of corn stover (Table 2). Other organic 

compounds made up 10 to 19% of the total and inorganics were 5-12% of the total mass. When 

the data has been adjusted for percent recovery and inorganic content, cellulosic components 

constitute 78-89% of the total organic biomass of corn stover, with an average concentration of 

84%. Data for wheat straw came from three sources, and data for this type of crop residue 

agreed very well with that for corn stover, with adjusted cellulosic compositions ranging between 

81% and 92%, with an average of 87%. EPA also considered the composition of sugarcane 

bagasse and straw from rice, soybeans, rye and barley, with data derived from one source for 

each biomass type except for sugarcane bagasse, which derived from two sources. Bagasse had 

an extremely high adjusted cellulosic composition of 94-98%. The composition of rice straw 

was very similar to that of both corn stover and wheat straw (Table 2). Both soybean straw and 

rye straw had cellulosic contents that were almost 10% lower than any other type of other crop 

residues (69% for both). However, for these samples, total lignin was not reported so we had to 

adjust the reported acid detergent lignin content using commonly observed relationships.4

 These 

numbers are accordingly only estimates and may in fact be much higher. Similarly, the 

calculated % cellulosic of the barley straw was 102%, which is physically impossible. We 

performed a similar adjustment of the acid detergent lignin content of this sample, so it is likely 

that we overestimated the lignin content of this sample. The average cellulosic content of all 

types of crop residues (excluding those with estimated lignin content) is 90%, with a range of 78-

 

f

 “Cellulosic Content of Various Feedstocks Spreadsheet – for the docket”, which has been placed in docket EPAHQ-OAR-2012-0401 
10 

98% (Table 2). These data suggest that on average around 85-90% of the organic mass of crop 

residues is composed of cellulose, hemicellulose and lignin, with crop residues generally 

containing more than 75% cellulosic materials. 

Table 2. Percent composition of crop residues, including percentages as reported (raw and 

unadjusted) for total cellulosic material, other organic materials and inorganics (ash) and 

cellulosic composition adjusted for percent recovery and presence of inorganics. 

      Reported Composition       

     

Cellulosic

Components

Other

Organics

Inorgan‐

ics (Ash)

Adjusted

Cellulosic

Composition Source

Crop Residue               

Corn Stover                

80% 10% 12% 89% DOE Database10

71% 19% 6% 79% Templeton et al. (2009)2

72% 20% 5% 78% Templeton et al. (2010)5

83% 11% 6% 88% Lee et al. (2007)4

Corn Stover Average 77% 15% 7% 84%    

Wheat Straw

74% 17% 10% 81% DOE Database

83% 7% 9% 92% NREL data11

82% 12% 6% 87% Lee et al. (2007)

Wheat Straw Average 80% 12% 9% 87%   

Other crop

residues

Rice Straw 74% n.d. 15% 86% Guo et al. (2009)12

Sugarcane Bagasse 90% n.d. 8% 98% Guo et al. (2009)

Sugarcane Bagasse 92% 6% 4% 94% Templeton et al. (2010)

Soybean Straw 65%* 29%* 6% 69%* Lee et al. (2007)

Rye Straw 65%* 29%* 6% 69%* Lee et al. (2007)

Barley Straw 91%*  ‐2%* 11% 102%* Lee et al. (2007)

Crop Residue Average 77% 14% 9% 90%   

*For these samples, lignin was reported as acid detergent lignin (ADL), which can be 

considerably lower than total lignin, which was reported for the other samples. Total lignin was 

estimated for these samples by multiplying ADL by 1.3 for soybeans (a legume) or by 3 for rye 

and barley (types of grass) as discussed in the text. These estimated values were not used in 

calculating the average. 

b. Grasses – Including Switchgrass and Miscanthus 

For our analysis of the chemical composition of grasses, EPA gathered information about 

switchgrass, miscanthus and twelve other types of grasses (Table 3). This included four studies 
11 

of switchgrass, three studies of miscanthus and one or two studies each of the remaining grasses. 

Of these grasses, switchgrass and miscanthus have been intensively studied for use as biofuels 

feedstocks. The composition of these two types of grasses were similar to each other, with the 

studies reporting switchgrass to contain 71-85% cellulosic components and miscanthus to have 

77-86% reported cellulosic materials. The average adjusted cellulosic compositions of both 

switchgrass and miscanthus are 85%. EPA has added energy cane as an allowable feedstock for 

cellulosic fuels under RFS in a recent rulemakingg, and giant reed and napiergrass have also been 

proposed as feedstocks for biofuels. These three grasses all had adjusted cellulosic compositions 

of 79-87% cellulosic. The adjusted cellulosic composition of the remaining grasses ranged from 

72% to 98%, although many of the studies only reported acid detergent lignin, requiring us to 

estimate total lignin content based on this number as discussed above, leading to greater 

uncertainty in the cellulosic content. However, cellulosic materials comprised greater than 70% 

of the adjusted mass of all of the grasses studied (Table 3). 

Table 3. Percent composition of grasses, including percentages as reported (raw and 

unadjusted) for total cellulosic composition, other organic materials and inorganics (ash) 

and cellulosic composition adjusted for percent recovery and presence of inorganics 

      Reported Composition       

     

Cellulosic

Components

Other

Organics

Inorgan‐

ics (Ash)

Adjusted

Cellulosic

Composition Source

Grasses                  

Switchgrass                

79% 17% 5% 82% DOE Database10

75% 15% 6% 83% NREL data11

71% 13% 7% 85% Dien et al. (2006)3

85% 9% 6% 90% Lee et al. (2007)4

Switchgrass Average 77% 14% 6% 85%   

Miscanthus

85% n.d. 4% 89% Guo et al. (2009)12

86% 12% 2% 88% Lee et al. (2007)

77% n.d. 1% 78%

Villaverde et al.

(2010)13

Miscanthus Average 83% 12% 2% 85%   

Other grasses                

Giant reed 83.5 n.d. 3.7 87% Scordia et al. (2011)14

 

g

 Regulation of Fuels and Fuel Additives: Identification of Additional Qualifying Renewable Fuel Pathways Under 

the Renewable Fuel Standard Program, 78 FR 14190, 14217 (March 5, 2013).. 
12 

Energy cane 75.2 19.6 5.2 79% BP data15

Napiergrass 83.4 13.1 3.5 86% BP data

Reed Canarygrass 58% 21% 11% 73% Dien et al. (2006)

Reed Canarygrass 66%* 26%* 8% 72%* Lee et al. (2007)

Big Bluestem 83% 11% 6% 88% Lee et al. (2007)

Tall Fescue 64% 25% 11% 72% Lee et al. (2007)

Indiangrass 86%* 6%* 8% 93%* Lee et al. (2007)

Little Bluestem (66%)† (27%)† 7% (71%)† Lee et al. (2007)

Prarie Cordgrass 92%* 2%* 6% 98%* Lee et al. (2007)

Intermediate Wheatgrass 82%* 12%* 6% 87%* Lee et al. (2007)

Smooth Bromegrass 86%* 6%* 8% 93%* Lee et al. (2007)

Timothy 73%* 21%* 6% 78%* Lee et al. (2007)

Other Grasses Average 78% 15% 7% 81%    

*For these samples, lignin was reported as acid detergent lignin (ADL), which can be 

considerably lower than total lignin, which was reported for the other samples. Total lignin was 

estimated for these samples by multiplying ADL by 3 as discussed in the text. These estimated 

values were not used in calculating the average. 

†Lignin was not measured for this sample, so these values are much lower than the true value. 

This sample was not used in calculating the average for grasses. 

c. Wood, Tree Branches and Leaves 

EPA gathered compositional data for wood from 10 different species of tree (Table 4), including 

seven hardwoods and three softwoods, as well as on two different samples of tree branches. The 

studies reported between 83 and 94% cellulosic components by mass for all woods and adjusted 

cellulosic compositions of 83 to 97%. The adjusted composition of the branch samples was very 

similar to that of the wood samples, with 86% and 89% cellulosic components, although one of 

the branch samples contained large amounts (18%) of inorganic materials, probably due to 

incorporation of non-branch materials such as soil. Two studies also determined the composition 

of samples of leaves and determined adjusted cellulosic compositions of 74% and 89%. The 

very high (37% by mass) proportion of inorganic materials in one of the leaf samples is almost 

certainly due to the inclusion of soil in the sample, as mentioned for the branch sample from this 

same study. The average adjusted cellulosic composition from woods and branches was 92%, 

whereas the value for leaves was 82%. 

Table 4. Percent composition of woods, tree branches and leaves, including percentages as 

reported (raw and unadjusted) for total cellulosic composition, other organic materials and 
13 

inorganics (ash) and cellulosic composition adjusted for percent recovery and presence of 

inorganics 

      Reported Composition       

     

Cellulosic

Components

Other

Organics

Inorgan‐

ics (Ash)

Adjusted

Cellulosic

Composition Source

Wood, Tree Branches & Leaves            

Black Locust 88% 8% 3% 92% DOE Database10

Eucalyptus 94% 3% 1% 97% DOE Database

Eucalyptus 83% n.d. 0% 83% Wang et al. (2007)16

Hybrid Poplar 89% 4% 1% 96% DOE Database

American Sycamore 87% 4% 1% 96% DOE Database

Eastern Cottonwood 88% 3% 1% 97% DOE Database

Yellow Poplar 89% 3% 2% 97% DOE Database

Red Oak 84% n.d. 0% 84% Wang et al. (2007)

Monterey Pine 91% 3% 0% 97% DOE Database

Radiata Pine 88% n.d. 1% 89% Wang et al. (2007)

Spruce 90% n.d. 2% 91% Wang et al. (2007)

Branches 86% n.d. 3% 89% Eleazer et al. (1997)8

Branches 70% n.d. 18% 86% Komilis and Ham (2003)9

Wood & Branches Average 88% 4% 1% 92%   

Leaves 86% n.d. 3% 89% Eleazer et al. (1997)

Leaves 47% n.d. 37% 74% Komilis and Ham (2003)

   Leaves Average 67% n.d. 20% 82%    

D. IMPLICATIONS FOR CELLULOSIC BIOFUELS 

In the March 2010 final RFS rule, EPA approved a number of feedstocks for production of 

cellulosic biofuels. In a subsequent rulemakingh

, we added energy cane to the list of approved 

feedstocks. These approved feedstocks are: 

Cellulosic biomass from crop residue, slash, pre-commercial thinning and tree 

residue, annual covercrops, switchgrass, miscanthus and energy cane; cellulosic 

components of separated yard waste; cellulosic components of separated food 

waste; and cellulosic components of separated MSW 

 

h

 Regulation of Fuels and Fuel Additives: Identification of Additional Qualifying Renewable Fuel Pathways Under 

the Renewable Fuel Standard Program, 78 FR 14190, 14217 (March 5, 2013). 
14 

In this rulemaking, we are also proposing to allow fuels produced from biogas from landfills to 

qualify as cellulosic biofuels. In this section, we discuss the cellulosic fraction of feedstocks that 

are already approved under RFS as part of a pathway eligible to generate cellulosic RINs.

To help this discussion, the data from Tables 2-4 above are summarized in Table 5. 

Table 5. Summary of Adjusted Cellulosic Composition for different types of feedstocks. 

Data are derived from Tables 2-4 above. 

Feedstock Type

Average

Adjusted

Cellulosic

Composition

Crop Residue 90%

Switchgrass 85%

Miscanthus 85%

Other Grasses 81%

Wood and Branches 92%

Leaves 82%

a. Crop Residues 

As discussed above, crop residues have an average adjusted cellulosic composition of 83% 

(Tables 2 & 5). With the exception of two samples for which we estimated lignin content, the 

adjusted cellulosic content was never lower than 78% of the total organic mass. Based on this 

analysis, it is clear that a large majority of the biomass of different types of crop residues is 

derived from cellulose, hemicellulose and lignin. 

The types of residues analyzed here are considered to be representative of the crop residue 

category as listed in Table 1 to § 80.1426. In the current Notice of Proposed Rulemaking 

(NPRM), “Modifications to Renewable Fuel Standard Program, E15 Misfueling Mitigation 

Regulations, and Ultra Low Sulfur Diesel Requirements,” we are seeking comment on the 

clarifications that crop residues be defined as: 

Crop residue is the biomass left over from the harvesting or processing of planted crops 

from existing agricultural land and any biomass removed from existing agricultural land 

that facilitates crop management (including biomass removed from such lands in relation 

to invasive species control or fire management), whether or not the biomass includes any 

portion of a crop or crop plant. Biomass is considered crop residue only if the use of that 
15 

biomass for the production of renewable fuel has no significant impact on demand for the 

feedstock crop, products produced from that feedstock crop, and all substitutes for the 

crop and its products, nor any other impact that would result in a significant increase in 

direct or indirect GHG emissions. 

Furthermore, Table IV.D.-1 to that NPRM also lists the feedstocks that would be considered 

under the crop residue category including: 

 Bagasse 

 Corn Kernel Fiber (excluding the corn starch component) 

 Corn Stover 

 Citrus Residue 

 Rice Straw 

 Wheat Straw 

We presented data specifically for corn stover, wheat straw, rice straw and bagasse in the 

previous section and anticipate that citrus residue would have a similar composition to the types 

of crop residue analyzed. For corn kernel fiber, as discussed in the NPRM, the percentage will 

vary, but as much as 20% of the final fuel could be derived from corn starch. By definition, corn 

starch ethanol can only qualify as a renewable fuel, not as an advanced fuel. 

b. Slash, Pre-Commercial Thinnings, and Tree Residue 

The March 2010 final RFS rule established the following definitions for slash, pre-commercial 

thinnings and tree residue: 

Slash is the residue, including treetops, branches, and bark, left on the ground after 

logging or accumulating as a result of a storm, fire, delimbing, or other similar 

disturbance. 
16 

Pre-commercial thinnings are trees, including unhealthy or diseased trees, removed to 

reduce stocking to concentrate growth on more desirable, healthy trees, or other 

vegetative material that is removed to promote tree growth. 

Tree residue is slash and any woody residue generated during the processing of planted 

trees from tree plantations for use in lumber, paper, furniture or other applications, 

provided that such woody residue is not mixed with similar residue from trees that do not 

originate in tree plantations. 

Based on these definitions, it is clear that woody material, ranging in size from tree trunks to 

branches to twigs, would comprise the majority of these feedstocks, along with some bark and 

likely some residual leaves. Based on the data in Tables 4 and 5, an average of 92% of wood and 

branches was cellulosic materials, and around 82% of leaves were composed of these 

compounds. Accordingly, EPA concludes that almost all of the material present in slash, precommercial thinnings and tree residue is composed of from cellulose, hemicellulose and lignin. 

c. Annual cover crops 

A January 2012 supplemental rulemakingi defined annual cover crops as follows: 

Annual cover crop means an annual crop, planted as a rotation between primary planted 

crops, or between trees and vines in orchards and vineyards, typically to protect soil from 

erosion and to improve the soil between periods of regular crops. An annual cover crop 

has no existing market to which it can be sold except for its use as feedstock for the 

production of renewable fuel. 

Common cover crops include a wide variety of types of plants, including different types of 

grasses and grains (e.g., buckwheat, oats, annual ryegrass, etc), legumes (e.g. clover, hairy vetch 

and field peas), and plants from the mustard family (e.g., arugula, forage radish and mustard).17 

 

i

 Regulation of Fuels and Fuel Additives: 2012 Renewable Fuel Standards; Final Rule, 77 FR 1320, 1358 (January 9, 

2012). 
17 

Because cover crops are so diverse, it is likely that their cellulosic content also varies widely. 

Accordingly, EPA has not attempted to constrain the cellulosic content of “cover crops”. 

Instead, we will consider the cellulosic content of cover crops on a case-by-case basis as we 

determine whether to approve that crop as a feedstock. 

d. Switchgrass 

As shown in Table 3, four different studies of switchgrass found adjusted cellulosic compositions 

of 82-90%, with an average of 85%, indicating that the vast majority of switchgrass biomass is 

composed of cellulose, hemicellulose and lignin. 

e. Miscanthus 

Similar to switchgrass, an average of 85% of miscanthus biomass is cellulose, hemicellulose and 

lignin (Table 3). 

f. Energy cane 

As discussed above, one analysis of energy cane found that it contained 79% cellulosic materials. 

g. Cellulosic components of separated yard waste; Cellulosic components of separated 

food waste; and Cellulosic components of separated MSW 

For these feedstocks we specifically outlined how they would be considered as part of the final 

rule published on March 26, 2010 (75 FR 14670). We reiterate this in the current NPRM. We 

determined that: 

Waste streams kept separate since generation from MSW that consist of yard waste are 

expected to be composed almost entirely of woody material or leaves, and therefore will 

be deemed to be composed of cellulosic materials. 
18 

Waste streams consisting of food wastes, however, may contain both cellulosic and noncellulosic materials. We will deem waste streams consisting of food waste to be 

composed entirely of non-cellulosic materials, 

For separated MSW, EPA is not aware of a test method that is able to distinguish 

between cellulosic- and starch-derived renewable fuel. Under these circumstances, EPA 

believes that it is appropriate for producers to base RIN assignment on the predominant 

component and, therefore, to assume that the biogenic portion of their fuel is entirely of 

cellulosic origin. 

This NPRM does not propose to change those determinations, therefore, biofuel produced from 

separated yard waste is considered to be 100% cellulosic, biofuel produced from the biogenetic 

portion of separated MSW is assumed to be 100% cellulosic, and biofuel produced from 

separated food waste is assumed to be non-cellulosic unless the producer demonstrates that some 

portion of the food waste is cellulosic. 

h. Biogas from landfills 

One research paper that examined the cellulosic origin of landfill biogas found that 91% of it 

derived from cellulose and hemicellulose.18 We discuss this conclusion in depth in a memo to 

the docket.j

 Accordingly, as with the other feedstocks examined in this memo, it appears that 

almost all of the landfill biogas is produced from cellulosic components. 

 

 

j

 “Support for Cellulosic Determination for Landfill Biogas and Summary of Lifecycle Analysis Assumptions and 

Calculations for Biofuels Produced from Landfill Biogas”, which has been placed in docket EPA-HQ-OAR-2012-

0401. 
19 

 

REFERENCES 

1

 Modified from U.S. Department of Energy - Energy Efficiency and Renewable Energy, 

Biomass Program, Feedstock Composition Glossary, Accessed December 3, 2012, 

http://www1.eere.energy.gov/biomass/printable_versions/feedstock_glossary.html. 

2

 Templeton, David W., Amie D. Sluiter, Tammy K. Hayward, Bonnie R. Hames, and Steven R. 

Thomas (2009) Assessing corn stover composition and sources of variability via NIRS. 

Cellulose, 16, 621-639. 

3

 Dien, Bruce S., Hans-Joachim G. Jung, Kenneth P. Vogel, Michael D. Casler, JoAnn F.S. 

Lamb, Loren Iten, Robert B. Mitchell, and Gautum Sarath (2006) Chemical composition and 

response to dilute-acid pretreatment and enzymatic saccharification of alfalfa, reed canarygrass, 

and switchgrass. Biomass and Bioenergy, 30, 880-891. 

4

 Lee, DoKyong, Vance N. Owens, Arvid Boe, and Peter Jeranyama (2007) Composition of 

herbaceous biomass feedstocks. Report prepared by North Central Sun Grant Center, South 

Dakota State University, SGINC1-07, 16 pp. 

5

 Templeton, David W., Christopher J. Scarlata, Justin B. Sluiter, and Edward J. Wolfrum (2010) 

Compositional analysis of lignocellulosic feedstocks: 2. Method uncertainties. Journal of 

Agricultural and Food Chemistry, 58, 9054-9062. 

6

 NREL (2011) Standard Biomass Analytical Procedure, Accessed January 8, 2012, 

http://www.nrel.gov/biomass/analytical_procedures.html 

7

 U.S. Department of Energy - Energy Efficiency and Renewable Energy, Biomass Program, 

Feedstock Composition Glossary, Accessed December 3, 2012, 

http://www1.eere.energy.gov/biomass/printable_versions/feedstock_glossary.html. 

8

 Eleazer, William E., William S. Ogle, III, Yu-Sheng Wang, and Morton A. Barlaz (1997) 

Biodegradability of municipal solid waste components in laboratory-scale landfills. 

Environmental Science & Technology, 31, 911-917. 

9

 Komilis, Dimitris P and Robert K. Ham (2003) The effect of lignin and sugars to the aerobic 

decomposition of solid wastes. Waste Management, 23, 419-423. 

10 Department of Energy, Energy Efficiencey & Renewable Energy, Biomass Program, Biomass 

Feedstock Composition and Property Database, Accessed December 6, 2011, 

http://www.afdc.energy.gov/biomass/progs/search1.cgi 

11 NREL data, email from Mary Biddy, National Renewable Energy Laboratory, National 

Bioenergy Center, on January 4, 2013. 

12 Guo, Gia-Luen, Deng-Chieh Hsu, Wen-Hua Chen, Wei-His Chen and Wen-Song Hwang 

(2009) Characterization of enzymatic saccharification for acid-pretreated lignocellulosic 

materials with different lignin composition. Enzyme and Microbial Technology, 45, 80-87. 

13 Villaverde, Juan José, Pablo Ligero and Alberto de Vega (2010) Miscanthus x giganteus as a 

source of biobased products through Organosolv fractionation: A mini review. The Open 

Agricultural Journal, 4, 102-110. 
20 

 14 Scordia, Danilo, Salvatore L. Cosentino, Jae-Won Lee, and Thomas W. Jeffries (2011) Dilute 

oxalic acid pretreatment for biorefining giant reed (Arundo donax L.). Biomass and Bioenergy 

35, 3018-3024. 

15 BP Crop Research Trial data, email from Ruth Scotti, BP Biofuels, February 13, 2013. 

16 Wang, Xiaoming, Jennifer M. Padgett, Florentino B. De la Cruz, and Morton A. Barlaz (2011) 

Wood biodegradation in laboratory-scale landfills. Environmental Science & Technology, 45, 

6864-6871. 

17 Cornell University College of Agriculture and Life Sciences. Cover Crop Guide, Accessed 

December 18, 2012, http://www.hort.cornell.edu/bjorkman/lab/covercrops/index.php 

18 Barlaz, Morton A., Robert K. Ham, and Daniel M. Schaefer (1989) Mass-balance analysis of 

anaerobically decomposed refuse. Journal of Environmental Engineering, 115(6), 1088-1102.